Magnetic fasteners



p 17, 1956 1.. c CRONBERGER MAGNETIC FASTENERS Filed March 26, 1952 INVENTOR mm c. GRONBERGER W ATTORNEY United States Patent 2,742,250 MAGNETIC FASTENERS Luther C. Cronberger, Tulsa, Okla.

Application March 26, 1952, Serial No. 278,640

1 Claim. (Cl. 248206) This invention relates to fasteners in general, more particularly to fasteners of the magnetic type, and the present patent application is a continuation-in-part of my co-pending patent application Serial No. 223,991, filed May 1, 1951, now abandoned.

A general object of my invention is to provide an improved fastener for supporting magnetizable objects on nonmagnetic structures.

A more specific object of my invention is to provide a fastener which can be secured to any desired nonmagnetic structure in the way of a tack and which has a high magnetic attractive power enabling it to firmly support against the action of gravity many different kinds of magnetizable objects.

Another object of my invention is to provide a magnetic fastener including a permanent magnet and a mag netic pole piece for the permanent magnet adapted to support magnetizable objects by magnetic attraction at a surface which is considerably larger than the cross-sectional area of the permanent magnet.

Further objects and advantages will readily become apparent upon a reading of the following specification taken in conjunction with the drawing, in which:

Fig. 1 is a cross-section of a magnetic fastener and a magnetizable object which is being supported by it against the action of gravity;

Fig. 2 shows the same structure as Fig. 1 in front view;

Fig. 3 is a top-plan view of a modified magnetic fastener;

Fig. 4 is a side view, partly in cross-section, of the fastener shown in Fig. 3; and

Figs. 5 and 6 are sectional front views of two magnetic fasteners in the shape of tacks.

According to this invention a magnetic fastener comprises a substantially rod-shaped element approximately of the same size, length and cross-sectional area as the shank of a small nail or screw. This rod-shaped element is arranged, or intended to be arranged in a bore provided in a nonmagnetic structure, e. g. of a wooden structure, and securely held therein. The magnetic fastener comprises also a magnetic head of considerably shorter length than the above referred-to rod-shaped element coaxially arranged immediately adjacent to one end of said rod-shaped element in engagement with the above referred-to nonmagnetic structure. Said magnetic head has a surface remote from said rod-shaped element having a considerably larger area than the cross-sectional area of said rod-shaped element. An object of magnetizable material is in physical engagement with and supported against the action of gravity by said magnetic head and the area of physical engagement between said head and said object exceeds the cross-sectional area of said element.

Referring now to the drawing, and more particularly to Figs. 1 and 2 thereof, reference numeral 1 designates a fixed structure of nonmagnetic material such as, for instance, wood. The structure to which numeral 1 has been applied may be considered to be a wooden panel.

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Four tacks, generally designated by numeral 2, are driven into the wooden structure 1. The heads 3 of tacks 2 have attractive magnetic power and firmly hold in position the iron or steel plate 5. Plate 5, in turn supports against the action of gravity a mirror 6, picture or the like which may be attached to its front surface by suitable adhesive means not shown. The shanks 4 of tacks 2 are formed by permanent bar magnets preferably made of a suitable aluminum nickel alloy such as that generally known in the trade as Alnico.

The fastener shown in Figs. 3 and 4 comprisesa small powerful permanent magnet 8 as, for instance, an Alnico rod of A inch diameter which is inserted into a hole 9 drilled into a block 1 of wood. The magnet 8 is loosely inserted into hole 9 but prevented from dropping out by a flat cap 10 which forms a pole piece for magnet 8. Magnet 8 is attracted to cap 10 and stays permanently in engagement therewith. The separate spherical cap 10 is cemented to block 1 by an adhesive 11.

The fasteners shown in Figs. 5 and 6 comprise a permanent shank-shaped magnet 8, preferably made of an aluminum nickel alloy and a head 10 made of a ferromagnetic material. Both may be bonded together by any suitable cement, i. c. any cement providing a sufficiently strong mechanical bond. The fastener shown in Fig. 5 has a spherically shaped hollow head of relatively thin cross-section and of such magnetic reluctance as to result in a substantial leakage flux along the surface thereof remote from shank 8. In the structure of Fig. 6 the magnetic head 10 is solid rather than hollow and most of the flux goes through the head, i. e. there is virtually no leakage flux at the surface of head 10 remote from shank 8. Some flux lines have been shown in Figs. 5 and 6 and indicated by reference letter F. Inasmuch as it is desired to cause the flux F originating at one pole of shank 8 to flow through another structure before returning to the other pole of shank 8, the arrangement of Fig. 5 is more desirable than that of Fig. 6. Accordingly the heads of the fasteners shown in Figs. 1 to 4, inclusive, should be hollow, as shown in Fig. 5.

It is possible and desirable to make up shank 8 of two parts, i. e. of an inner core element which is a permanent magnet and an outer sleeve element which is nonmagnetic and adapted to be driven into a Wooden or the like nonmagnetic body. The sleeve element may be screw-threaded, if desired.

It will be observed from the foregoing that the magnetic portion of my fasteners intended to be in physical engagement with the object to be supported by magnetic attraction is large, i. e. considerably larger than the cross-sectional area of the rod-shaped portion of the fastener which projects into the nonmagnetic material by which the fastener is supported. This is an important feature because the holding power of the fastener increases within limits with the size of this area of engagement. For this reason the radius of curvature of the pole piece 10 should be relatively large, as best shown in Fig. 4. The joint magnetic flux through the permanent magnet 8 and the magnetic head or pole piece 10 is always sufficiently large to preclude relative movement under the actions of gravity and accidental impact forces between said pole piece and the object of magnetizable material which is being supported by it.

The geometrical configuration of the magnetic field is different depending upon whether the pole piece is fiat or convex, as shown in Figs. 3 to 6. I have found that the convex type of pole piece is preferable, i. e. that fasteners which are provided with convex pole pieces have a considerably increased attractive or holding power. In such pole pieces the holding surface follows more closely an equipotential plane, resulting in a more even distribution of the magnetic flux over the holding surface,

Whereas if the holding surface is flat, this tends to result in an undue concentration of the magnetic flux along the circumference of the pole piece.

Although I have shown and described specific structures it is to be clearly understood that the same were merely for the purpose of illustration and that changes and modifications may readily be made herein by those skilled in the art Without departing from the spirit and scope ofthe appended claim.

I claim as my invention:

A magnetic fastener comprising a shank portion and a separate spherical hollow head portion in abutting relation with said shank portion, said shank portion consisting of a permanently magnetic material and said head 4 portion consisting of a magnetizable sheet material magnetized by said shank portion to such high degree of saturation as to result in a substantial leakage flux along the surface thereof remote from said shank portion.

References Cited in the file of this patent UNITED STATES PATENTS 32,527 Nichols et'al. June 11, 1861 10 2,203,580 Ronning June 4, 1940 2,495,644 Rowley Ian. 24, 1950 2,510,634 Hull June 6, 1950 2,570,626 Abraham Oct. .9, 1951 2,627,778 Hodell Feb. 10, 1953 

